Is a main() required for a C program?

Question

Well the title says it all. Is a main() function absolutely essential for a C program?

I am asking this because I was looking at the Linux kernel code,

Answer 1

In machine language things get executed sequentially, what comes first is executed first. So, the default is for the compiler place a call to you main method to fit the C standard.

Your program works like a library, which is a collection of compiled functions. The main difference between a library and a standard executable is that for the second one the compiler generates assembly code which calls one of the functions in your program.

But you could write assembly code which calls your an arbitrary C program function (the same way calls to library functions work, actually) and this would work the same way other executables do. But the thing is you cannot do it in plain standard C, you have to resort to assembly or even some other compiler specific tricks.

This was intended as a general and superficial explanation, there are some technical differences I avoided on purpose as they don't seem relevant.